Intramolecular meta photocycloaddition of conformationally restrained 5-phenylpent-1-enes. Part II: Steric and electronic effects caused by 4-mono- and 4-disubstitution

Article abstract of DOI:10.1016/0040-4020(95)00374-H

The meta photocycloaddition of 4-substituted 5-phenylpent-1-enes. 10-18, has been studied. The monosubstituted derivatives always prefer 2,6 addition, independent of the size of the substituent. For 2,6 addition two basic conformations are possible. Disubstituted compounds yield predominantly 1,3 addition with the sterically more demanding group exo. Except for the methoxymethyl and THF derivative the oxygen is found exo as a result of repulsion, while the monohydroxy derivative gives also endo which might be explained by hydrogen bonding. The products from compound 11 change from mainly endo-OH in cyclohexane to chiefly exo-OH in methanol. Much similarity is found with Diels-Alder cycloaddition.